Donald Trump famously canceled a missile strike on Iran in June, but Tehran will not be resting easy following the unpredictable president's warning that the United States is again "locked and loaded."After giving diplomats whiplash last week with reversals on Afghanistan, Trump now has the world on tenterhooks over his response to a weekend attack on Saudi oil facilities that his top diplomat has blamed on Iran."We'll see?" he tweeted Monday in a phrase that encapsulated the lack of clarity.Just last week, the White House dangled out the possibility of a meeting between Trump and President Hassan Rouhani, which would mark an extraordinary thaw in US-Iranian relations.Even though the Iranians showed little sign of being ready, Trump aides and Trump himself hinted at openness to at least an informal encounter during the UN General Assembly in New York next week.As Secretary of State Mike Pompeo said: "The president has made very clear he is prepared to meet with no preconditions."Then came Saturday's attack by drones setting ablaze oil processing facilities in Saudi Arabia, both a close US ally and a bitter enemy of Iran.Iranian-backed Huthi rebels fighting Saudi-backed forces in Yemen claimed responsibility. The Saudis and Pompeo pointed the finger at Tehran, which in turn insisted it was not responsible.The intensifying back and forth put Trump in the role of referee and, as is his style, he's leaving the players in suspense.On Sunday, Trump tweeted "there is reason to believe that we know the culprit" and he warned the United States was "locked and loaded depending on verification."On Monday, he moved closer to blaming Iran directly, while still leaving a little wiggle room.Claiming that Iran told "a very big lie" in June when it said it downed a US spy drone because it had violated its airspace, he tweeted: "Now they say that they had nothing to do with the attack on Saudi Arabia. We'll see?"'Smart' or 'tough?' It was in June, after the US drone downing, that Trump ordered a retaliatory bombing raid against Iran, only to say he'd called it off with 10 minutes to go. He said the dramatic reversal was made after learning 150 people could die, which he saw as out of proportion.That moment of restraint - which some critics said had more to do with chaotic decision making than the president's sense of humanity - fit in with Trump's promise to keep the United States out of unnecessary wars.After two decades of military quagmires in Afghanistan and Iraq, this was one of the factors in 2016 that fueled Trump's appeal to voters looking to break the status quo.But Trump is just as keen to show toughness abroad.It's a contradiction that came to a head on September 7 when after months of painstaking negotiations with the Taliban, Trump surprised everyone by announcing he had wanted to meet personally with the insurgents near Washington.In the same tweet he revealed the even greater surprise that he'd canceled the meeting at the last minute because of a Taliban bomb attack a few days earlier, in which one American soldier died.Subsequently Trump clarified that the peace talks were being scrapped altogether.Which Trump is at the controls now over Iran?"We not only have the fog of war in the Middle East as to the attacks on Saudi oil, but also the fog of foreign policy when it comes to the United States," warned Richard Haass, president of the Council on Foreign Relations.In the wake of the Taliban turmoil, Trump fired his national security advisor John Bolton, whom he had frequently described as too bellicose.Bolton, a major advocate of the war in Iraq, had long supported overthrowing Iran's government, so his departure fed speculation that the more dovish Trump was in the ascendant.Trump, though, seemed to bristle at suggestions that his sacked advisor had been too "tough" for him, saying it was also important to be "smart."Trump is clearly not averse to military force.He has boasted repeatedly in the last week that US forces are hitting the Taliban "harder than ever" -- even though there is no evidence in public to support the claim.But Iran, which has a sophisticated military and controls much of the oil shipping lane through the Strait of Hormuz, presents a far more dangerous challenge.